like whether tax rates can be lowered without adding to the deficit. >> not mathematically possible. >> it is mathematically possible. it's been done before. it's precisely what we're proposing. >> it has never been done before. >> it's been done a couple of times, actually. >> it has never been done before. >> jack kennedy lowered tax rates, increased growth. ronald reagan -- >> oh, now you're jack kennedy? >> reporter: biden went right at ryan over mitt romney's controversial comments calling 47% of americans who don't pay income taxes irresponsible. >> the idea, if you heard that, that little sol little quill on 47%, you think he just made a mistake, then i got a bridge to sell you. >> i think the vice president very well knows sometimes the words don't come out of your mouth the right way. >> but i always say what i mean. >> reporter: when biden wasn't talking, he seemed oddly amused. by our count -- smiling or breaking out in laughter 92 separate times. expressive, often interrupting and occasionally personal. >> this is a bunch of stuff. look, here's the deal. >> what does that